/Engine/Source/Runtime/Engine/Classes/Engine/SkeletalMesh.h
Force the creation of a new GUID use to build the derive data cache key. Next time a build happen the whole skeletal mesh will be rebuild. Use this when you change stuff not in the skeletal mesh ddc key, like the geometry (import, re-import) Every big data should not be in the ddc key and should use this function, because its slow to create a key with big data.
void InvalidateDeriveDataCacheGUID()